Method of making 1, 3, 5-hexatriene



nited States Patent-O METHOD OF MAKING 1,3,5-HEXATRIENE James M. Shackelford and Louis H. Schwartzman, Pittsburgh, Pa., assignors to Koppers Company, Inc., a corporation of Delaware -No Drawing. Filed Feb. 16, 1959, Ser. No. 793,299

8 Claims. (Cl. 260-682) This invention relates to a method of making 1,3,5- hexatriene. In one specific aspect, it'relates to a novel catalytic dehydration of 1,4-hexadiene-3-ol to give 1,3,5- hexatriene in yields greater than those obtainable by prior art methods.

1,3,5-hexatriene polymerizes readily to give a high melting polymer. It can be combined with styrene and/or butadiene to form heat resistant polymers of high impact strength. Because of the considerable commercial potential of high impact polymeric materials made from 1,3,5-hexatriene, a need exists for a method of making this useful compound from the least expensive ofthe hexadiene-ols, viz: 1,4-hexadiene-3-ol.

Heretofore, 1,3,5-hexatriene has never been successfully prepared by the dehydration of 1,4-hexadiene-3-ol. In the past, certain of the isomeric hexadiene-ols have been dehydrated to give 1,3,5-hexatriene in yields which are relatively low when considered from a commercial standpoint. For example, Woods and Schwartzman, J. Am. Chem. Soc., 70, 3394 (1948), reported the dehydration of 1,3-hexadiene-5-ol in the presence of alumina at a temperature of 325-350 C. under reduced pressure (1.0 mm.) to give a 64% yield of 1,3,5-hexatriene.

The preparation of 1,3,5-hexatriene from 1,3-hexadiene- 5-01 involves only a simple dehydration, since the hydroxyl group is adjacent to a carbon atom containing a removable hydrogen atom. Thus, the splitting oil of water results in the direct formation of the conjugated triene, 1,3,5-hexatriene. The dehydration of 1,4-hexadiene-3-ol presents an altogether different problem. In the case of this particular carbinol, both of the carbon atoms adjacent to the carbon atom containing the hydroxyl group are doubly bonded to adjacent carbon atoms (i.e. vinyl groups flank the carbinol). Thus, 1,3,5-hexatriene can only be produced from this hexadiene-ol by a molecular rearrangement of the diene-ol coupled with a dehydration. Prior attempts to accomplish this rearrangement-dehydration of 1,4-hexadiene-3-ol to 1,3,5- hexatriene have been unsuccessful. Prevost, Bull. Soc. Chim., 1409 (1955), attempted to make 1,3,5-hexatriene by passing the 1,4-hexadiene-3-ol over alumina at 300? C.

He obtained cyclohexadiene in almost quantitative yields as his only identifiable product.

l,4hexadiene-3-ol is preferable to the other hexadiene CC A a' novel method of making 1,3,5-hexatriene from 1,4- hexadiene-S-ol in yields as high as 90-95%.

In accordance with the invention, 1,4-hexadiene-3-ol is contacted in the vapor phase with a dehydration catalyst comprising a major portion of either silica or alumina and having a surface area of about 50-150 square meters per gram. The rearrangement-dehydration is accomplished simultaneously using a reaction temperature of about 225 350" C. and a pressure ranging from a reduced pressure of one millimeter of mercury to atmospheric pressure. Contact between the vapors of 1,4- hexadiene-3-ol and the catalytic material is maintained for not more than about 4 seconds. The vapors are condensed and the product 1,3,5-hexatriene, boiling at 79-80 C., is recovered therefrom in substantially pure form. Further purification, if desired, can be effected by recrystallization. Any unreacted carbinol can be recycled and combined with the feedstock for subsequent dehydration.

The method of the invention depends upon the careful control of such variables as catalyst activity, temperature, pressure and contact time. Catalyst activity is controlled primarily by the surface area of the particular catalyst used, although it is affected to some extent by the chemical composition of the catalyst. When catalysts having a higher activity are used, lower temperatures and shorter contact times provide the best yields of 1,3,5-hexatriene. The contact time selected is influenced measurably by temperature and pressure, as well as by catalyst activity. Generally speaking, higher temperatures of dehydration require a shorter contact time. At

atmospheric pressure the required contact time is greater able and lower in cost than those required for the preparation of the other hexadiene-ols.

1,4-hexadiene-3 -01 is made in excellent yield by the reduction of 4-hexene-1-...'.. yne-3-ol in the presence of a palladium on calcium carbonate catalyst containing lead, acetate. The 4-hexene-1-yne-3- 01 is made by the well-known reaction of sodium acetylide and crotonaldehyde. a novel method of accomplishing simultaneously the necessary rearrangement-dehydration of 1,4-hexadiene-3- 01 to give 1,3,5-hexatriene in yields greater than those obtainable by any prior art method.

It is, therefore, an object of the invention to provide Quite surprisingly,'we have found mote effective rearrangement-dehydration. Above about than that required when reduced pressures are used.

The choice of a catalyst for purposes of the invention is predicated on the activity of the particular catalyst selected. As we have already noted, the activity of the catalyst is influenced to a greater degree by the surface area thereof than by its chemical composition. Suitable catalysts comprise a major portion (at least 50% by weight) of either silica or alumina. Thus, the catalyst may be activated alumina, silica-alumina or any one of a number of naturally occurring siliceous or aluminous materials commonly employed as dehydration catalysts. The so-called promoted dehydration catalysts which comprise a silica, silica-alumina or alumina base and a minor portion (0.5 to 10% by weight) of a metal oxide, such as the oxides of thorium, iron, Zinc, chromium, barium, copper, nickel, and cesium, are useful in the invention. The silica, silica-alumina or alumina catalyst body may also be promoted with various phosphates and borates.

The catalyst may be used in either pelleted or granular form and the particle size thereof is not particularly critical. We have found it convenient to use pellets having a diameter ranging between inch and inch or described hereabove, we can control the catalyst activity to the required extent by regulating the surface area of the particular dehydration catalyst selected. If the surface area of the catalyst used exceeds about 150 square metersip'er gram, such a catalyst is too active and the yields of 1,3,5-hexatriene obtainable are markedly diminished. The high yields of the invention are obtained using a catalyst having a surface area of about 50-150 square'fmeters per gram. A catalyst having a surface area of about to square meters per gram is preferred.

, The reaction temperature can vary widely. A minimum temperature of about 225 C. is required to pro- 3. 350 C. only low yields. of the desired product are. ob.- tained. As we have already pointed out, when more active catalysts are used, it is desirable to operate in the lower portion of the permissible temperature range. This 4 EXAMPLE II A Pyrex glass tube (29 mm. ID.) was packed with a silica-alumina catalyst comprising 87% silica and 13% alumina inch pellets) for a length of six inches. A

is also true when longer Contact times are i F preheat zone of five inches of glass beads was used and Preferred temperatures for the method of the inventlon a thermocouple well (4, an) was placed in the range between about 290 and 300 center of. the tube. The. tube was externally heated to The control of pressure for purposes of the lnvention 2500 C; and the System was excited through a Dry Ice is less important than the control of the other variables. trap and a vacuum Pump maintain the desired pressure The process can be conducted effectively at atmospheric (5400 mm"). pressure or at reduced pressures as low as 1 mm. of l4 hexadiene 3 ol (49 g, 05 m.) was distilled into mercury We have found h l i although not the reactor over. a period of 40 minutes at a pressure of necessary, to conduct the reaction in an inert atmosphere 30 mm. This was calculated to give a Contact time in such as nitrogen the range of 0.05-0.25 second. The vapors were con- Control of the contact time is of particular importance. densed and the water (85 g) 1 3 s hexatriene (332 g If the contact time between the catalyst and the vapors and unreacted i l (4,1 g) were separated. The of the 1S extqnded beymld about 4 hydrocarbon fraction was analyzed by means of gas seconds, the y eld of 1,3,5-hexatr1ene begins to decrease chromatography and found to contain 88 mole percent mafkedly- Usmg a Contact i 9 seconds wlth an of 1,3,5-hexatriene, 5 mole percent of 1,3-cyclohexadiene, active catalyst no 1,3,5-hexatr1ene is recovered as a prod- 0 35 mole parcel. of benzene and traces of other hydn} uct. At atmospheric pressure the preferred contact time carbons Th ultimate yield of pur 1 3 S- atrien ranges between about 1.5-3.0 seconds. Under reduced was pressures a contact time of 0.05-0.25 seconds is preferred, EXAMPLE In although longer contact times (l-2 seconds) can be used with only a very slight reduction in yield. Contact time 25 Uslhg h apparatus described Pref/10115 examples, is conveniently controlled by the physical arrangement 1,4'heXadlene-3-01 Was dlstlned Into the feaetel of the catalyst bed. We prefer to use a vertical bed and at The Vapors Were condensed and uhrefleted either pass the feed vapors downwardly through the bed cal'hlhol 23-), Water g) and or alternatively, draw the vapors upwardly through the Wel'e p The hydrocarbon fraehon W213 bed using reduced pressures. Using a vertical fixed bed, ahalyhed y means of mass Speethometrl and found 9 the contact time can be directly controlled by the bed eohtalh 94 mole P 0f 1, 3,5-heXatfleI1e- The Ultlthickness and feed rate. mate yield of pure 1,3,5-hexatr1ene was 92%.

Our invention is further illustrated by the following EXAMPLE IV exam les.

p EXAMPLE I Using the apparatus described in the previous examples, 1,4-hexad1ene-3-ol (49 g.) was pumped through the reac- A Pyrex glass tube (29 mm. ID.) waspa d Wlth tor at atmospheric pressure at such a rate as to give a alumma (1A3 Inch pellets) for a length of 51x mches- A contact time-of 1.5 seconds. The vapors were condensed preheat zone of five lnches of glass beadswas used and and unreacted carbinol (195 g), water (50 and a thermocouple well (4 mm. CD.) was placed 1n the 1,3,5-hexatriene (22.5 g.) were separated. The hydrocenter of the tube. The tube was externally heated to carbon fraction was analyzed by means of gas chmma 290-300 and the System was excltFd through a D tography and found to contain 80 mole percent 1,3,5- Ice trap and a Vacuum pump to mamtam the desired hexatriene and various other hydrocarbons such as benpressure (STIOO zene and 1,3-cyclohexadiene. The ultimate yield of pure 1,4-hexad1ene-3-ol (49 g., 0.5 m.) was distilled into the 1,3,5hexatriene was 745% reactor f a period of 40 F at a i 30 The recovered carbinol was analyzed and found to be Thls was calculated to glve a Contact the identical with the starting 1,4-hexadiene-3-ol. Therefore, range of (ms-0'25 Second The vapPrs were condensed the rearrangement-dehydration reaction seems to be a and the Water, l3s'hexatnene (358 and concerted, rather than consecutive, process. unreacted carbinol (2.2 g.) were separated. The hydrocarbon fraction was analyzed by means of gas chroma- EXAMPLE V tography and found to contain 92 mole percent 1,3,5- Following the procedure of the previous examples, a hexatriene, 4 mole percent 1,3-cyclohexadiene, 2 mole series of runs was made to determine the influence of the percent benzene and traces of other hydrocarbons. The critical process variables on the ultimate yield of pure ultimate yield of pure 1,3,5-hexatriene was 86%. The product. The results are shown below in Table I.

Table I PREPARATION OF 1, 3, 5==HEXATRIENE Catalyst Reaction Pressure, Contact Yield, Run Temperamm.ot Hg Time, percent No. Composition Surface Area, ture, C. sec.

sq. meters/g.

1 87% Silica-13% 150-170 300 760 24 11.7

Alumina.

150-170 300 30 0. 4 04. 8 270-300 300 760 25 0. 0 270-300 300 760 5. 6 15. 0 80-100 350 32 0. 16 71. 3 80-100 350 760 1. 35 e3. 7 80-100 425 760 1. 25 11. 6 80-100 300 30 0. 2 84. 6 80-100 300 1. 6 es. 6 -100 300 7. 5 0. 10 71. a

physical properties of pure 1,3,5-hexatriene are B;P. 79.6-80.0 C./760 mm., F.P. -8.06 C., n 1.5088, eat 2565 A. 48,400.

The data of Table I clearly show that when the critical limits of temperature, contact time and catalyst surface 5 area are exceeded, only very low yields of 1,3,5-hexatriene can be obtained. Run 3 is especially noteworthy in that it shows that under adverse conditions of catalyst activity and contact time no 1,3,5-hexatriene is obtained.

We claim:

1. Method of making 1,3,5-hexatriene comprising contacting 1,4-hexadiene-3-ol with a dehydration catalyst comprising a major portion of a material selected from the group consisting of silica and alumina having a surface area of about 50-150 square meters per gram at a temperature of about 225-350 C. and at a pressure of about 1-760 mm. of mercury for not more than about 4 seconds.

2. Method of making 1,3,5-hexatriene comprising contacting 1,4-hexadiene-3-ol with an alumina dehydration catalyst having a surface area of about 50-150 square meters per gram at a temperature of about 275-350 C. and at a pressure of about 1-760 mm. of mercury for not more than about 4 seconds.

3. Method according to claim 2 wherein said temperature is 290-300 C.

4. Method according to claim 2 wherein the surface 2 area of said catalyst is 80-100 square meters per gram.

5. Method of making 1,3,5-hexatriene comprising contacting 1,4-hexadiene-3-ol with a silica-alumina dehydration catalyst having a surface area of about 50-150 square meters per gram at a temperature of about 225-300 C.

and at a pressure of about 1-760 mm. of mercury for not more than about 4 seconds.

6. Method of making 1,3,5-hexatriene comprising contacting 1,4-hexadiene-3-ol with an alumina dehydration catalyst having a surface area of about -150 square meters per gram at a temperature of about 225-350 C. for about 1-3 seconds.

7. Method of making 1,3,5-hexatriene comprising contacting 1,4-hexadiene-3-ol with an alumina dehydration catalyst having a surface area of about 50-150 square meters per gram at a temperature of about 225-350" C. and at a pressure of about 1-75 mm. of mercury for about 0.05-0.25 second.

8. Method of making 1,3,5-hexatriene comprising contacting l,4-hexadiene-3-ol with a dehydration catalyst comprising a major portion of a material selected from the group consisting of silica and alumina having a surface area of about -100 square meters per gram at a temperature of about 290-300 C. and at a pressure of about 5-760 mm. of mercury for not more than about 4 seconds, condensing the hydrocarbon vapors thus formed and recovering substantially pure 1,3,5-hexatriene therefrom.

References Cited in the file of this patent Butz: Journal of American Chemical Society, volume 64, 1942, pages 1978-1979.

Woods et al.: Journal of American Chemical Society, volume 77, 1955, pages 1800-1801.

Prevost et al.: Bull., Soc. Chimique de France, 1955, pages 1408-1410. 

1. METHOD OF MAKING 1,3-5-HEXATRIENE COMPRISING CONTACTING 1,4-HEXADIENE-3-OL WITH A DEHYDRATION CATALYST COMPRISING A MAJOR PORTION OF A MATERIAL SELECTED FROM THE GROUP CONSISTING OF SILICA AND ALUMINA HAVING A SURFACE AREA OF ABOUT 50-150 SQUARE METERS PER GRAM AT A TEMPERATURE OF ABOUT 225-350*C. AND AT A PRESSURE OF ABOUT 1-760 MM. OF MERCURY FOR NOT MORE THAN ABOUT 4 SECONDS. 